This invention relates to a mixture of trialkyl phosphine oxides as an extractant for the recovery of organic acids from aqueous solutions.
Recovery of acid from aqueous solution is extensively practiced in industry. Organic acids, such as citric acid, malic acid, tartaric acid and oxalic acid, have been commercially produced by fermentation or by chemical synthesis. Because of impurities existing in fermentation broths, the acid is precipitated as a calcium salt and is liberated by adding sulfuric acid so as to obtain pure organic acid solution. Then, the final product of the acid is obtained after evaporation and crystallization. This procedure has the disadvantages of requiring expendable lime and sulfuric acid as well as disposal of calcium sulfate.
A liquid-liquid extraction process by means of different extractants and techniques, known as an alternative means of recovery of organic acid from aqueous solution, has also been proposed in the prior art.
Procedures which employ amines are disclosed in British Pat. No. 1,428,018 and U.S. Pat. No. 2,539,472. U.S. Pat. No. 3,944,606 disclosed the use of amines to produce citrate. Because of the lower selectivity of amines, the symbiosis acid, such as oxalic acid, from fermentation would be co-extracted into solvent of amine during the process of extraction, and the unknown toxicity of amines limits their use for edible purposes.
The phosphoryl-containing extractant is also used by the invention of U.S. Pat. No. 3,816,524 and Japan Pat. No. 47-5715. However, expensive centrifugal equipment has to be used in treating the emulsion existing in the extraction of fermentation broth.
U.S. Pat. No. 4,571,671 discloses the use of amides to extract citric acid and European Pat. No. 0,049,426 discloses a mixture of amines and water immiscible organic acid as solvent.
The present invention develops a process for the recovery of organic acid from aqueous solution by extraction. The fermentaton broth containing the organic acid is pretreated by active carbon in order to prevent emulsion, then the pretreated aqueous solution is extracted without emulsion in any equipment, such as a Mixture-settler and several columns. The extractants are phosphoryl-containing compounds, wherein a mixture of trialkyl phosphine oxides (HTRPO) which is not disclosed by any prior art is more suitable, because of its better extraction ability and selectivity as well as good adaptability for various processes in the extraction and stripping.
Furthermore, none of the prior art suggests the process in which the citric acid for edible and pharmaceutical purposes is recovered from fermentation broth by extraction.